A bumper beam for a vehicle

ABSTRACT

A bumper beam has a bow-formed outer profile ( 14 ), that has a central flange ( 16 ) and two webs ( 15, 18 ) and is fastened in two crash boxes ( 12, 13 ) with its central flange face away from the crash boxes. The outer profile has a cover ( 15 ) so that the bumper beam will have a closed profile. The cover ( 15 ) has a central flange ( 24 ) and two webs ( 25, 26 ). The webs ( 17, 18 ) of the outer profile ( 14 ) are jointed in pairs with the webs ( 25, 26 ) of the cover ( 15 ), and the web height of the cover at its centre is bigger than the web height of the outer profile ( 14 ) at its centre.

This invention relates to a bumper beam for a vehicle, comprising anouter profile with a bow-formed central flange and two webs and a coverthat provides a closed profile, the outer profile being adapted to befastened with its central flange facing outwards from the vehicle.

BACKGROUND OF THE INVENTION

A bumper beam that has good properties for various kinds of barriercrashes may be bad for a collision with a pole at a low velocity. One ofthe most common accidents involving a rear bumper beam, for example, isthe crash against a lamp post on a parking lot. In particular when thebumper beam is fastened in crash boxes that are weak sideways, thebumper beam will collapse locally and fold.

Object of invention

It is an object of the invention to provide a bumper beam that has goodperformance generally and also good performance in a low velocity crashagainst a pole. This is achieved when the cover has a central flange andtwo webs, and the webs of the cover are coupled in pairs with the websof the outer profile, the web height of the cover at its centre beinggreater than the web height of the outer profile at its centre.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a bumper beam.

FIG. 2 is a side view of the same bumper beam as seen from inside thevehicle.

FIG. 3 is a section taken along line 3-3 in FIG. 1.

FIG. 4 is an enlargement of a portion of FIG. 1.

FIG. 5 is a perspective view of one of the parts that make up the bumperbeam of the preceding figures.

DESCRIPTION OF THE ILLUSTRATED AND PREFERRED EXAMPLE OF THE INVENTION

FIG. 1 shows, as seen from above, a bumper beam 11 of steelsymmetrically fastened in two crash boxes 13, only one of which beingillustrated and only schematically. The bumper beam is made up of anouter profile in the form of a bow-formed beam 14 and a cover 15. Theouter profile is a hat profile as shown in FIG. 3 with a central flange16 and two webs 17,18 that end in side flanges 19,20. The centralportion of the central flange may have a longitudinal stiffener 21, thedepth of which decreases from its centre so that it ends at 22. Thecover 15 is also in the form of a hat profile with a central flange 24and two webs 25,26 that end in side flanges 27,28. The webs of the twohat beams are united by welds. The webs can be directly welded togetheror altematively, they can be united by having their side flanges 19,20;27,28 welded together as illustrated. As can be seen in FIG. 3, thesheet thickness of the cover is less than the sheet thickness of theouter profile. The steel of the cover may also have lower yield strengththan the steel of the outer profile. The outer profile can suitably bepress-hardened, that is, hot stamped and hardened in the same tools inone operation, whereas the cover can suitably be cold formed fromcold-forming sheet steel. The outer profile may have a sheet thicknessof 2 mm and a yield strength of about 1150 MPa or more, whereas thecover may have a considerably less sheet thickness and a yield strengthof less than 3/4 of the yield strength of the outer profile, for exampleabout half the strength. The sheet thickness of the cover may suitablybe at most ¾of the thickness of the outer profile.

The cover 15, that is, the inner profile, is shown in perspective asFIG. 5. Its webs 25,26 has transverse stiffeners 23 and the height ofthe webs reduces continuously so that the cover ends a flat sheet.

As best shown in FIG. 4, the crash boxes 13 have a fastening plate 29with holes for screws so that they can be screwed to a supportingportion of the vehicle. They have a fastening plate 30 as well in whichthe outer profile is fastened, preferably being welded thereto. Theplate 30 has a portion 31, which is bent outwards and under which theflat end of the cover extends and is welded to the portion 31 so thattension forces can be transmitted between the plate 30 and the cover.Alternatively, the cover may extend under the entire plate 30 and bewelded both to the plate and to the outer profile. In both cases, theouter profile 14 is fastened in the crash boxes, either directly orindirectly with the cover in between. Since the cover may be made ofcomparatively thin sheet, its fastening to the crash boxes may be tooweak in the absence of the plate 30 and such a plate 30 is thereforepreferred.

The central flange 24 of the cover has linear extension between thecrash boxes and the depth of the bumper beam at its middle is largerthan its depth at its fastening portions. The depth relation should beat least 130% or rather at least 160%. The central flange 24 of thecover takes the tension load when the outer profile hits for example apost and it reduces the risk of local collapsing of the outer profile14. Instead of collapsing, the bumper beam will have a dent. If thetension load would not be taken up, the outer profile 14 would tend tostraighten out and bend the crash boxes outwards. At high a collisionload, the crash boxes would bend outwards from each other and then, theycould not deform as intended and could therefore not take up energy asintended. The central flange of the cover need not be exactly linear inorder to take up tension load well. It should, however, be substantiallylinear, and a bow form with a pitch of a few cm has a minor effect onthe capability of taking up tension load.

The depth of the outer profile increases continuously from the centre ofthe bumper beam towards the fastening portions, which provides for aweight reduction and a cost reduction since, without disadvantage, thecover can have a thinner sheet thickness and a lower strength than theouter profile. The strength of the cover calculated as a combination ofyield strength of the material and the sheet thickness may be less thanhalf the corresponding strength of the outer profile. The stiffeners 23or corrugation of the webs 25,25 of the cover reduces the risk of thewebs collapsing.

1. A bumper beam for a vehicle, comprising an outer profile (14) with abow-formed central flange (16) and two webs (17, 18), and a cover (15)that provides a closed profile, the outer profile being adapted to befastened with its central flange facing outwards from the vehicle,characterised in that the cover (15) has a central flange (24) and twowebs (25, 26), and the two webs (25, 26) of the cover are coupled inpairs with the two webs (17, 18) of the outer profile (14), the webheight of the cover (15) at its centre being greater than the web heightof the outer profile (14) at its centre, the web height of the outerprofile (14) increasing continuously sideways from its centre, and theweb height of the cover (15) decreasing continuously sideways from itscentre.
 2. (canceled)
 3. A bumper beam according to claim 1,characterised in that the depth of the bumper beam at its centre is atleast 130% of the depth of the bumper beam at its fastening portions,and the central flange (24) of the cover extends substantially linearlybetween these fastening portions.
 4. A bumper beam according to claim 3;characterised in that its depth at its centre is at least 160% of itsdepth at its fastening portions.
 5. A bumper beam according to claim 1,characterised in that the webs of the cover have transverse stiffeners(23).
 6. A bumper beam according to claim 1, characterised in that theouter profile (14) and the cover (15) are welded together.
 7. A bumperbeam according to claim 6, characterised in that both the outer profile(14) and the cover (15) have side flanges that end their webs, and theseside flanges (19 and 27; 20 and 28) are welded together.
 8. A bumperbeam for a vehicle, comprising an outer profile (14) with a bow-formedcentral flange (16) and two webs (17, 18), and a cover (15) thatprovides a closed profile, the outer profile being adapted to befastened with its central flange facing outwards from the vehicle,characterised in that the cover (15) has a central flange (24) and twowebs (25, 26), and the two webs (25, 26) of the cover are coupled inpairs with the two webs (17, 18) of the outer profile (14), the webheight of the cover (15) at its centre being greater than the web heightof the outer profile (14) at its centre, and the sheet of the cover hasa lower yield strength than the sheet of the outer profile.
 9. A bumperbeam for a vehicle, comprising an outer profile (14) with a bow-formedcentral flange (16) and two webs (17, 18), and a cover (15) thatprovides a closed profile, the outer profile being adapted to befastened with its central flange facing outwards from the vehicle,characterised in that the cover (15) has a central flange (24) and twowebs (25, 26), and the two webs (25, 26) of the cover are coupled inpairs with the two webs (17, 18) of the outer profile (14), the webheight of the cover (15) at its centre being greater than the web heightof the outer profile (14) at its centre, and the sheet thickness of thecover (15) is less than the sheet thickness of the outer profile (14).10. (canceled)
 11. (canceled)
 12. A bumper beam according to claim 3,characterised in that the webs of the cover have transverse stiffeners(23).
 13. A bumper beam according to claim 4, characterised in that thewebs of the cover have transverse stiffeners (23).
 14. A bumper beamaccording to claim 3, characterised in that the outer profile (14) andthe cover (15) are welded together.
 15. A bumper beam according to claim4, characterised in that the outer profile (14) and the cover (15) arewelded together.
 16. A bumper beam according to claim 5, characterisedin that the outer profile (14) and the cover (15) are welded together.17. A bumper beam according to claim 8, characterised in that the thesheet thickness of the cover (15) is less than the sheet thickness ofthe outer profile (14).
 18. A bumper beam according to claim 9,characterised in that the sheet of the cover has a lower yield strengththan the sheet of the outer profile.
 19. A bumper beam according toclaim 8, characterised in that the depth of the bumper beam at itscentre is at least 130% of the depth of the bumper beam at its fasteningportions, and the central flange (24) of the cover extends substantiallylinearly between these fastening portions.
 20. A bumper beam accordingto claim 9, characterised in that the depth of the bumper beam at itscentre is at least 130% of the depth of the bumper beam at its fasteningportions, and the central flange (24) of the cover extends substantiallylinearly between these fastening portions.
 21. A bumper beam accordingto claim 8, characterised in that the webs of the cover have transversestiffeners (23).
 22. A bumper beam according to claim 9, characterisedin that the webs of the cover have transverse stiffeners (23).
 23. Abumper beam according to claim 8, characterised in that the outerprofile (14) and the cover (15) are welded together.